In stationary or rotary anode tubes, or else metal jet x-ray tubes, there is the problem of the power density at the point of incidence of the electron beam on the anode component. There, too high power losses are generated for given luminous intensities and focal spot luminances. Moreover, strong background magnetic fields, for example caused in conjunction with magnetic resonance imaging scanners, cause a problem. It is impossible to electrostatically focus the electron beam in magnetic fields of such strength.
The problem of maintaining the solid or liquid aggregate state of the anode material in the focal point of the electron beam in rotation anode tubes and in metal jet x-ray tubes is solved by virtue of the material of the rotary anode or of the metal jet being transported sufficiently quickly through the focal spot at the focal point of the electron beam. In the process, the electrons are decelerated to a standstill, even though only high-energy electrons cause the desired short-wave x-ray radiation. In view of the focal spot power deposition, and also in view of the efficiency, the complete deceleration is a disadvantageous process.